How To Identify Dandelions

I posted previously about Dandelions, how they may be very good food to eat, being both high in nutrients, and good for your health. As promised, here is a (somewhat complex perhaps) guide to figuring what is and isn't a Dandelion. Following the table, I treat each group in details. The table can serve as a good reference - even though it is, as yet, incomplete.
Please note that there may be other plants growing in Ireland which may superficially resemble Dandelions, also that Dandelions have up to 250 species growing in the UK and Irl, which would require someone well versed in their nuances to identify them (a similar story as the Brambles/Blackberries). The common Dandelion's scientific name (Taraxacum officinale), thus, is given as an agglomeration of the species. It technically doesn't really exist.

	Cat's Ear	Hawk's Beard	HawkBit	Hawkweed	True Dandelion
Stem branching	some	frequent	never	frequent	never
Stem fluted*	no	deeply			no
Stem hollow	no	?	no		yes
Stem Latex	?	?	no	yes	yes
Leaves	Rosette + stem bracts.	Rosette + stem leaves (latter deeply lobed, spiny with auricles)	Rosette only - long and straight leaves	Rosette and often stem too. Depends on species.	Rosette only
Leaf lobes	rounded	Deep lobes	Bluntly lobed		toothed/unlobed
Leaf midrib	Tinged purple	red			Varying colour
Hairs	Leaves only	Rough – bristly!	v. hairy stem	variable	hairless
Outter Ray Florets*	orange/reddish stripe	orange/reddish stripe on some.		variable	normal yellow
Disk Florets*	In centre	Each with 2 hair-like projections	None (?)	none	none
Sepals	Of varying lengths, with scales	Same lengh with bracts beneath.	No scales		Same length; sometimes with bracts forming a ring
Fasciation*	Succeptable	?	?	?	Succeptable
Seed head	Brownish white	Slightly grey-white		White	White
Max height	60cm	65cm	50cm	variable	50cm
Edibility?	Yes	Yes, mildly bitter	Yes	At least one species edible.	Yes, almost always bitter

Table of some of the features of Dandelions and their look alikes

Cat's Ear Example (source)

Cat's Ear: Smooth (Hypochaeris glabra – rare in Irl) or regular (H. radicata – freq in Irl). Perennial. Flowers rarely fully open (except maybe in strong sun) and have disk florets at the centre. The leaves of the 'normal' species are hairy, not those of the smooth species. Flowering stems have scale-like bracts (like cat's ears) just below the flower head, but no leaves except the basal rosette. The seed head ('seed clock') has an off-white, brownish colour. More information: WildFlowerFinder; Edibility and medicinal information: PFAF and MiddlePath. 

Hawk's Beard Example (source)

Hawk's Beard (Crepis spp.): Beaked, Rough, Smooth and March species are common in Ireland. Annual. Easily distinguished by a double row of spreading bracts below the sepals. 'Beaked' and 'Smooth' species have an orange-red stripe on the outer ray florets. Stem is often deeply fluted* with red tinge, or mostly red. Leaves with few but strong hairs (can pierce skin!). Few basal (rosette) leaves. More information: WildFlowerFinder. Apparently it is edible, but with little or no medicinal usage: PFAF.

Photo L. hispidus (source)

 HawkBit/Leontodon: Both Rough (Leontodon hispidus) and Lesser (L. saxatilis) Hawkbit are frequent in Ireland. Perennial. Possibly one of the closer 'look-alikes' to Dandelion in appearance, with similar diuretic effect and it is edible raw or cooked according to PFAF. Some distinguishing features include: forked (t-shaped) hairs, leafless stems - leaves only in rosette, like dandelion (and cat's ear but without bracts), no latex and undivided stems. 

 Photo H. umbellatum (source)

Hawksweed (Hieracium spp./agg.): There are many different Hawksweed species found in Ireland and more in Britain. They are a notoriously difficult group to classify. Some information on Wikipedia to illustrate this: Wikipedia also see anatomy. The good news is that they don't seem to be toxic (in case you mistake it for a dandelion or similar), with at least one species edible, according to PFAF. 

Photo Dandelion (source)

True Dandelion (Taraxacum officinale): Perennial, frequent throughout Ireland. Dandelions are best distinguished by a combination of: basal (rosette) leaves only – which are hairless and (usually) tooth-lobed; undivided flowering stems with no bracts or leaves – the stems being both hollow and latex containing; flowers contain ray florets only without red colouration – the sepals have the same lenght with bracts forming a ring around the base. The entire plant is usually hairless and usually bitter tasting. Dandelions have many edible and medicinal uses, see Plant For A Future page for more details: PFAF. Apparently there are up to 250 varieties/species belonging to 9 sections to be found (at least in the UK, 8 sections are found in Ireland), but being very similar they need an expert to distinguish. The significance of this is that it is, in theory, possible to find a dandelion flowering at any time of the year (however any given plant does not flower all year around!). More information on this at WildFlowerFinder.

Glossary 
Ray Florets:  "(in a composite flowerhead of the daisy family) Any of a number of strap-shaped and typically sterile florets that form the ray. In plants such as dandelions, the flowerhead is composed entirely of ray florets" – The Free Dictionary.com
Disk Florets: "(in a composite flowerhead of the daisy family) Any of a number of small, tubular, and usually fertile florets that form the disk. In rayless plants such as the tansy, the flowerhead is composed entirely of disk florets" – The Free Dictionary.com
Fluted Stem: Deep ridges and furrows running vertically up the stem.
Fasciation: where the normal flower development is interrupted (can be due to either a mutation, infection, herbicide use etc.) and so the flower develops in an oval form, or maybe as a double head. This is possible in many flowers, but common only in a few (such as Dandelion, Willow and Foxglove).